Fittings are used for connecting the ends of either rigid or thinwall conduit. Fittings include connectors which connect the conduit to a box, and also couplings which connect two lengths of conduit to one another. There are two basic types of fittings, namely the compression type fitting, and the set screw type fitting. The set screw type fitting has certain practical advantages, namely it is less expensive to manufacture and it is quicker in installation time. Furthermore, it may be used in close quarters where there would not be room to apply a wrench to a compression fitting.
Compression type fittings are readily rendered raintight, or water resistant. The advantages of raintightness will be obvious. In addition, such fittings can be made relatively airtight, and this is an advantage in some construction projects in which fish tape is moved through a length of conduit by air pressure differential, generally by application of compressed air at one end, and often by vacuum assist at the other end. The fish tape is then used to pull a large number of wires through the conduit simultaneously.
Heretofore set screw type fittings have been unsatisfactory as to raintightness and as to air leakage, making it difficult to blow a fish tape through a long length of conduit connected with set screw type fittings. Since the set screws are applied from one side only, the conduit and the fittings necessarily end up slightly eccentric relative to one another. Coupled with this, in a case of a 4-inch diameter conduit the outside diameter of the conduit may vary as much as 0.040 inch, while the inside diameter of the fitting may vary 0.020 inch. Such errors in nominal dimension may be cumulative, providing as much as 0.060 inch error.
The object of the present invention is to provide a rubber or plastic boot on one or both ends of a conduit fitting to render the connection between the fitting and the conduit raintight, and relatively airtight.